The present invention relates to an information recording medium used in an optical disk.
There are known various principles of recording information on a thin film (recording film) by laser beam irradiation. Among them, a principle utilizing a change in atomic arrangement by the laser beam irradiation, such as a phase change (also called a phase transition or a phase transformation) of a film material, is hardly subjected to deformation of the thin film, thus having an advantage of obtaining an information recording medium having a double-sided disk structure obtained by sticking two disk members together directly.
Generally, such an information recording medium has a constitution in which a first protective layer, a recording film of GeSbTe series and the like, an upper protective layer and a reflective layer are provided on a substrate. In JP-A-2001-266408, description is made concerning that (ZnS)60(SiO2)30C10 is used as a first protective layer and a film thickness thereof is set in the range of 50 nm to 400 nm.
Note that, in the present specification, the term “phase change” is used including not only a meaning of phase change between a crystalline state and an amorphous state but also melting (a change to a liquid phase), recrystallization and a phase change between two crystalline states. Moreover, mark edge recording is a recording method for making an edge portion of a recording mark correspond to a signal “1” and making between marks or inside the mark correspond to a signal “0”. In the present specification, an optical disk refers to a disk, in which information reproducible by light irradiation is recorded, and/or to a device for reproducing information by the light irradiation.